The human oral cavity is usually colonized by more than 800 different germs which are in a natural equilibrium with one another. This microflora which substantially consists of bacteria, however, also comprises organisms which can damage the health of teeth. This relates in particular to bacteria that are able to metabolize carbohydrates from the diet to organic acids. The acid, in particular lactic acid, attacks the tooth enamel, which leads first to a demineralization of the tooth surface. Owing to continuous colonization of the demineralized sites, in the course of time, lesions result which can attack through the tooth enamel to the dentine and the pulp.
The majority of the lactic acid responsible for caries is due to the metabolic activity of “mutans streptococci”; this group includes the species S. mutans, S. sobrinus, S. rattus and S. cricetus. In addition, the group of the lactobacilli is of importance in this context. Whereas these bacteria, together with differing other bacterial species that colonize the oral cavity, are in a healthy state in a stable equilibrium, under special conditions increased multiplication of mutans streptococci can occur, as a result of which the risk of developing caries considerably increases. The acid formation caused by mutans streptococci leads to an acid environment that in turn increasingly promotes the growth of lactobacilli. An increased growth of lactobacilli is accompanied by a further lowering of the pH, owing to the acid production by lactobacilli, which promotes progress of the disorder.
It has been found that within a few minutes after supply of a sugar solution, the pH in the plaque falls greatly owing to the fermentative activity of the bacteria colonizing the oral cavity. However, it was found in a clinical study that plaque samples from children who had detectable caries, and plaque samples from caries-free children had a comparable potential of lowering the pH in the oral cavity (Minah & Lösche, Infection and Immunity, 17: 43-54, 1977). This is an indication that, in the human oral cavity, in addition to streptococci and lactobacilli, there is a number of other microorganisms which, although they excrete acid as metabolic by-products, do not present a significant risk of caries. Consequently, measuring the entire acid production in saliva is unsuitable for determining the number of cariogenic bacteria and therefore the caries risk of a patient. Rather, this risk is decisively determined by the concentration of the mutans streptococci and lactobacilli.
The quantitative or semi-quantitative determination of mutans streptococci and/or lactobacilli in the plaque or saliva can give information on the caries risk of a patient. For this reason, test methods have been developed that provide an investigation of plaque or saliva samples with respect to the concentration of the germs by plating them out on selective nutrient media. For instance, the test system obtainable as CRT© bacteria from Ivoclar Vivadent is based on the selective enrichment of mutans streptococci or lactobacilli from saliva samples on nutrient agar plates. Saliva samples are streaked onto respectively bacitracin-containing Mitis Salivarius agar (selective for streptococci) and in parallel thereto onto Rogosa agar (selective for lactobacilli). By enumerating the colonies formed on the agar plates after incubation for two to three days, a statement can be made on the respective caries risk of the patient. Similar systems are also available as Dentocult from Orion Diagnostics and as Caricult from OralBiotech.
However, culturing saliva samples on nutrient media is time-consuming. Customarily, the results cannot be assessed until about two to three days after plating out the saliva sample. It is therefore an object of the present invention to provide a method with which a statement can be made with respect to the number of cariogenic bacteria in a plaque or saliva sample reliably and reproducibly in a short time. The method should be able to be carried out without complex apparatus and the result should be available within a few hours, if possible.